The long term objectives of this research plan are to apply contemporary electrophysiological and pharmacological techniques to obtain an improved understanding of the mechanisms responsible for atrial flutter and to develop an improved basis for the treatment of atrial flutter. The specific aims of the research plan include: the development of a canine model for the study of atrial flutter; the mapping of the sequence of atrial activation during spontaneous and induced atrial flutter; the utilization of transient entrainment and interruption of atrial flutter during overdrive atrial pacing to study the nature and mechanism of atrial flutter; the localization of the area of slow conduction and unidirectional block which is a part of the ostensibly reentrant atrial flutter loop; the study of the effects of edrophonium chloride and N-acetylprocainamide on the cycle length of atrial flutter; the study and further characterization of Type Ii atrial flutter and its relationship with Type I atrial flutter; the study of the efficacy of introducing premature atrial beats simultaneously at two separate sites as a means of interrupting atrial flutter; the study of the efficacy of surgical treatment of atrial flutter. The methods to be used include: the use of cardiac pacing and recording atrial electrograms and ECGs in patients during open heart surgery, during cardiac catheterization, and following open heart surgery. The methods also include aseptic surgery to create sterile pericarditis in the canine heart in order to develop a chronic model for atrial flutter. The scientific disciplines involved include cardiac electrophysiology, pharmacology, and surgery. The health-relatedness of the project is clear in that atrial flutter is a well known, troublesome, and poorly understood abnormality affecting patients in significant numbers. The proposed studies should provide important new information to assist in improved diagnosis and treatment of patients suffering from this abnormality